Maritime floating hoses for drawing-off oil consist of a manifold complex and reinforced inner layer, of a foam which imports the enclosing and a floating ability, the synthetic foam being provided with a coating sheet closing the whole system from outside. Hose production could usually be divided into two main parts: after having built up completely the inner reinforced hose system, prior to applying the foam layer the system is subjected to heat treatment and fully vulcanized; thereafter, during a second main phase the foam layer is applied and thus the outer coating sheet is formed, which is then separately vulcanized.
This separation of processes is imperative, as the most important physico-mechanicl characteristics of the foam layer to be used and the desired large specific volume are all temperature-dependent. Specific volume of the floating layer, when it is formed of thermoplastic synthetic foam, is reduced considerably and in an irreversible manner even if heat-treatment is performed under an insignificant pressure; however, this kind of curing is indispensable for vulcanizing a 3-5 mm thick rubber coating a floating foam layer may be formed by using a special shaping technology, e.g. local "in situ" foaming of a on polyurethane. However, this method is seldom more economical than building up the hose from a roll, well adaptable to a plurality of hose sizes, whereby the foam layer is formed by winding the elastic foam-sheet with closed cells. Accordingly, the pivotal question of production of floating hoses for drawing-off oil is to what extent thermal load--i.e. temperature of thermal curing and/or duration of heat treatment--needed for the formation of the outer coating above the foam layer can be reduced.
According to the British Patent Specification GB-PS No. 1 202 094 the problem of avoiding considerable compression of the thermoplastic foam layer in course of the second heat treatment is solved in the course of hose building by applying above the foam layer a further special stiff (helical) reinforcing layer to prevent compression of the foam layer. This reinforcing element may be a high-strength spiral made of a fiber-reinforced reactive synthetic material (e.g. of a glassfiber-twist with an epoxy resin as binding material). However, when evaluating this technically doubtless good but most expensive solution, it should be considered that said reinforcing means scarcely contributes to the vacuum or pressure tolerance of the oil transporting hose, i.e. to the most important operative parameters. As these parameters are to be achieved in functional/inner/hose itself. In the British Patent Specification it is proposed to build-up the reinforcing means in the inner hose layer by using a steel-wire system.
According to the British Patent GB-PS No. 1 239 397 in the inner functional system of the swimming hose a glassfiber-reinforced synthetic spiral is inserted.
Protection of the semi-stiff synthetic foam against compression is solved by placing the synthetic foam into the interspaces between the rubber layers which have been wound helically from an extruded rubber sheet with a rectangular cross-section, while maintaining keeping a considerable distance between the adjacent turns. Applied also from a sheet-roll, in a helical form. It is quite obvious that this solution is satisfactory except for the introduction of foam in a restricted layer thickness. One of the most important features of the maritime hoses for drawing off oil,--ability to float--is also considerably restricted.